It is usual to allow the head to bend forward easily and naturally during the transmuting exercise.
(10) BRAIN STIMULATING.
The Yogis have found the following exercise most useful in stimulating the action of the brain for the purpose of producing clear thinking and reasoning.

It has a wonderful effect in clearing the brain and nervous system, and those engaged in mental work will find it most useful to them, both in the direction of enabling them to do better work and also as a means of refreshing the mind and clearing it after arduous mental labor.
Sit in an erect posture, keeping the spinal column straight, and the eyes well to the front, letting the hands rest on the upper part of the legs.

Breathe rhythmically, but instead of breathing through both nostrils as in the ordinary exercises, press the left nostril close with the thumb, and inhale through the right nostril.

Then remove the thumb, and close the right nostril with the finger, and then exhale through the left nostril.

Then, without changing the fingers, inhale through the left nostril, and changing fingers, exhale through the right.